The Long Term Evolution (LTE) architecture is a standard for wireless communication of high-speed data for mobile phones and data terminals. LTE provides an upgrade path for service providers with both Global System for Mobile Communications (GSM)/Universal Mobile Telecommunications System (UMTS) networks and Code Division Multiple Access 2000 (CDMA 2000) networks. In LTE, a base station, known as an evolved Node B (eNodeB), receives data and signaling information over an air interface from mobile terminals (e.g., smart phones, etc.), referred to as user equipment (UE), that are connected to the eNodeB within a geographical area called a cell. The eNodeB transmits the data and signaling information over a physical medium (e.g., fiber links) to a core network (i.e., network elements independent of the connection technology of the mobile terminal). Also, the eNodeB wirelessly transmits data and signaling information received from the core network to the UEs. Traditionally, a Node B in a UMTS terrestrial radio access network (UTRAN) has minimum functionality, and is controlled by a Radio Network Controller. However, with a LTE eNodeB, there is no separate controller element. This simplifies the architecture and allows lower response times.
In LTE networks, UEs measure the reference signal received power and the reference signal received quality from base stations/eNodeBs. In addition, the UEs will report to the eNodeB to which it connects (i.e., a serving eNodeB) all of the base stations/eNodeBs that it detects in neighboring cells that operate on the same carrier frequency, including neighboring cells that are not part of the eNodeB's Neighbor Relation Table of neighboring cells. Base stations in neighboring cells of a serving base station/serving eNodeB, virtual base stations and distributed base stations are referred to herein as neighbor relations.
After the UEs report identifiers of the other base stations in neighboring cells to the serving eNodeB, the serving eNodeB may automatically update the Neighbor Relation Table to include identifiers of previously unknown neighbor relations, automatically initiate an X2 link to an eNodeB in a neighboring cell, and automatically update the Neighbor Relation Table to include the new X2 link. The X2 link is an interface for connecting neighboring eNodeBs in a peer to peer fashion that allows the eNodeBs to communicate and to perform hand-offs without assistance from the core network. A hand-off is the process in which the radio access network changes the radio transmitters or radio access mode or radio system used to provide the bearer services, while maintaining a defined bearer service quality of service.
There are a fixed number of X2 links that an eNodeB can support. Disadvantageously, in densely populated urban areas that have macro cells (i.e., outdoor base stations with a large cell radius), metro cells (i.e., base stations that are mounted on lamp posts, positioned on the sides of buildings or found indoors in stadiums, transport hubs and other public areas), and femtocells (i.e., small, low-power base stations typically designed for use in a home or small business), UEs may report potential neighbors that exceed the maximum number of X2 links that an eNodeB can support. When X2 links are not added to an eNodeB's Neighbor Relation Table, calls may be dropped and re-established, resulting in degraded network performance.
Also, disadvantageously, since the use of X2 links may result in lower signaling overhead, a lower number of X2 links at an eNodeB may indicate that a network may not be optimized and run efficiently. Further disadvantageously, some neighbor relations and X2 links in an eNodeB's Neighbor Relation Table may not be used. Current solutions purge the neighbor relations and the X2 links that have not been used periodically via a garbage collection mechanism that purges them after a predetermined number of days, which may not be fast enough to prevent network degradation.